Environmental radioactivity studies

at NED-NTUA

Marios Anagnostakis

Nuclear Engineering Department, National Technical University of Athens,

15780 Athens, GREECE

managno@mail.ntua.gr http://nuclear.ntua.gr

Outline

� History of environmental radioactivity studies at NED-

NTUA

� Equipment and techniques used, Q/A protocols applied

� Research today at NED-NTUA and future plans

History of environmental radioactivity

studies at NED-NTUA

Chernobyl fallout mapping

� A total of 1242 samples of 1cm thick surface soil were collected all over

Greece during the period from May to November 1986.

� The sampling covered the most populated areas of the mainland

(~92300km2).

� In several cases repetitive samplings were conducted at the same location,

either simultaneously or at a later period, resulting several hundred samples.

� A total of ten Chernobyl fallout radionuclides (137Cs, 134Cs, 125Sb, 106Ru, 144Ce,110mAg, 54Mn, 95Zr, 103Ru and 141Ce) were determined and mapped

� At several sites a second 1cm thick soil layer sample, at the depth of 10cm

was also collected in the period 1986-1992 in order to study the vertical

migration of 137Cs.

� Three natural radionuclides existing in the soil (226Ra, 232Th and 40K) were also

determined and mapped.

Chernobyl fallout mapping

Natural radioactivity mapping

Determination of radionuclides emitting low

energy photons

� The analysis of the existing samples and

not only for radionuclides emitting low-

energy photons was the next step

� Need for a Low energy photon detector

(LEGe)

� Need for self absorption correction of

photons within the sample

� Permitted the accurate determination

and mapping of radionuclides such as 210Pb, 234Th (238U) and 241Am

Mapping of 238U and 210Pb

Dose rate due to terrestrial gamma radiation

from natural radionuclides

� Knowledge of the distribution of

the main natural radionuclides

(226Ra, 232Th and 40K) in Greek

surface soil allowed the

estimation of the gamma ray

dose rate due to the natural

radionuclides of terrestrial

origin.

� This dose rate was

experimentally verified.

Lead-210 in soil is of particular importance for

many reasons

� It is produced from 226Ra existing in the soil

(supported 210Pb)

� It is produced in the air from the decay of 222Rn exhaling from the ground

(unsupported 210Pb)

� It has a characteristic vertical profile which

can be used to study the transport of

surface soil associated with erosion and

sedimentation

� As all radionuclides deposited in the ground

it presents a size fraction in the soil

210Pb in soil

Equipment and techniques used, Q/A

protocols applied

Analytical techniques available at NED-NTUA

� High resolution gamma spectrometry (It is the workhorse of radioactivity measurements at NED-NTUA)

� Radon measurements (radon indoors measurements, exhalation measurements from the ground and materials, radon in water)

� Alpha spectrometry

� Liquid scintillation

� Total α-β measurements

� Neutron activation analysis

� X-ray fluorescence

The gamma spectroscopic analysis isperformed using for detector systemsof NED-NTUA:

� HPGe (34% rel ef., 1.78keV at 1322keV)

� LEGe (2000 mm2 active area, fwhm=341eV at 5.9keV).

� XtRa (104.5% rel. eff., fwhm=1003eV at 122keV)XtRa-CSS)

� HPGe (40% rel. ef.)

Gamma spectrometry

1 0 0 1 0 0 0

1 E -3

0 .0 1

0 .1 G e o m e try V o lu m e 2 8 2 c m3

M a te r ia l : 4 M H C l

D e te c t o r 2 : G e r m a n iu m D e te c t o r (G e )

D e te c to r 1 : G e r m a n iu m L ith iu m D e t e c to r ( G e L i)

Eff

icie

ncy

D e t e c to r 4 : E x t r a R a n g e G e r m a n iu m D e te c to r (X tR a )

D e te c t o r 3 : L o w E n e r g y D e te c t o r (L E G e )

E n e rg y ( k e V )

� The XtRa detector is coupled to a Compton Suppression System for background reduction and improvement of detection limits

� This result to the reduction of measurement uncertainty in environmental samples and permits the analysis of low volume samples (10-20cm3) with good accuracy

Gamma spectrometry

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0

0

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

6 0 0 0

Πλήθος καταγραφόμενων παλμών

Ε ν έ ρ γ ε ια (k e V )

φ ω τ ο κ ο ρ υ φ ή 1 3 7

C s

σ τ α 6 6 1 .6 2 k e V

In-situ gamma spectrometry

In situ measurements using a BEGe detector

Soil vertical profile - sampling

� Easy to sample when soil is hard

� Soil profile may be disturbed

� Extraction of soil not very easy

� Power supply is required

� Depth profiles are determined by sampling with a core sampler.

� For good depth resolution (~1 cm) the amount of sample collected per slice is low

(~45cm3).

� The amount of sample may be further reduced due to the presence of stones, etc.

� Collecting multiple samples is time and labor intensive.

Small sample geometries

are essential!

Soil vertical profile sampling

Soil and sediments samplings and in–

situ measurements

� 24 hours air-drying

� Sieving with a sieving machine for

20 mins

� Weighing

� Moisture content measurement

� Sealing with silicon

� Painting with epoxy resin

Soil sample preparation

I2

u1

Slide 19

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QA/QCNED-NTUA is

� A member of the IAEA ALMERA Network and for more than two decades

participates 1-2 times per year in radioactivity measurements Proficiency

Tests and Intercomparison Exercises

� A member of the International Committee for Radionuclide Metrology

(ICRM) and participates in the Gamma Spectrometry Working Group

Intercomparison Exercises and publications

Research today at NED-NTUA

and future plans

Geometry optimization for 210Pb

determinationMean

Radius

(cm)

Height

(cm)

Volume

(cm3)

A 1.25 1.73 9.1

B 1.61 1.70 14.5

C 1.69 2.73 24.6

D 1.41 1.99 12.6

E 2.59 1.20 24.1

F 2.65 1.34 27.6

G 2.40 1.89 34.1

H 2.85 0.64 17.9

I* 3.57 1.00 40.0

J* 3.75 2.20 97.2

Size fractionation of radionuclides in the soil

Uranium series radionuclides vertical distribution

234Th (238U)

� Activity is more or less constant with depth

226Ra

� Equilibrium with 234Th close to the surface

� Significant disruption of equilibrium between the three radionuclide in the deep soil

210Pb

� Significant decrease with depth, close to equilibrium with 226Ra

0

10

20

30

40

50

60

70

80

90

100

110

120

130

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Ac

tivit

y c

on

ce

tra

tio

n(B

q/k

g)

depth (cm)

URANIUM SERIES RADIONUCLIDES

Pb-210

Th-234

Ra-226

Slide 24

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210Pb

� Decreasing activity concentration in larger particles. A significant amount of the 210Pb detected in the surface soil comes from the atmosphere, as a decay product of atmospheric 222Rn (unsupported 210Pb).

226Ra

� Disruption of radioactive equilibrium between 234Th and 226Ra, indicating that 226Ra is not produced locally by the decay of 238U, but is brought in the area, probably with the water.

Uranium series radionuclides size fractionation

Sampling of radioactive aerosols

� High volume air sampler F&J DH-50810E

� Glass fiber 8x10” FP810M air filter

� Air sampling from 2h to 10 days depending on the

application

� Total air volume up to 20000m3

� Analysis for the determination of 210Pb, 7Be, 22Na

Future plans

� The techniques which have been developed and tested over the years for

the analysis of environmental samples in the ground and the air have proven

to provide very good quality results, in terms of type A and type B

uncertainty as well as detection limits, even for small sample volumes.

� Therefore, it is believed that techniques and models (like MODERN) which

are based on the use of natural or artificial radionuclides like 210Pb, 137Cs,7Be, 22Na as tracers of environmental processes (sedimentation, erosion, air

masses transport etc) may be easily applied at NED-NTUA in the future to

provide reliable results.